1. Field of the Invention
The invention relates to an Internet communications system, and more particularly relates to a system that manages the transport of voice over the Internet.
2. Description of the Background
A "call" occurs when two or more parties communicate or exchange information using telephony equipment. The large installed base of personal and office computers and the recent explosion of Internet use has expanded the universe of telephony equipment beyond the conventional telephone system.
With conventional telephony, a telephone set is used to originate and receive telephone calls. The telephone set is connected to a central office exchange that contains switching equipment, signaling equipment and batteries that supply direct current to operate the telephone. When the handset of the telephone is resting in its cradle, the weight of the handset holds the switchhook buttons down. The circuit between the telephone handset and the central office exchange is open. This is called the on-hook condition. When the handset is removed from its cradle, the spring-loaded buttons come up and the switchhook closes. This completes the circuit to the central office exchange and current flows in the circuit. This is called the off-hook condition. The off-hook signal tells the central office exchange that someone wants to make a call. The central office exchange returns a dial tone to the calling phone to let the caller know that the exchange is ready to accept a telephone number. The telephone set sends the telephone number by dial pulses if it has a rotary dial or by audio tones if it has a push-button keypad.
The central office exchange has various switches and relays that automatically connect the calling and called phones. If the called phone handset is off-hook when the connection is attempted, a busy tone generated by the central office exchange is returned to the calling phone. Otherwise, a ringing signal is sent to the called phone to alert the called party that a call is waiting. At the same time, a ringback tone is returned to the calling phone to indicate that the called phone is ringing.
When the called party removes the handset in response to a ring, the loop to that phone is completed by its closed switchhook and loop current flows through the called telephone. The central office exchange then removes the ringing signal and the ringback tone from the circuit.
The part of the telephone into which a person talks is called the transmitter. It converts speech (acoustical energy) into variations in an electric current (electrical energy) by varying or modulating the loop current in accordance with the speech of the talker. The part of the telephone that converts the electric current variations into sound that a person can hear is called the receiver. The signal produced by the transmitter is carried by the loop current variations to the receiver of the called party.
The call is ended when either party hangs up the handset. The on-hook signal tells the central office to release the line connections.
Thus far, the discussion of connecting two telephones together has been limited to local loops and a central office exchange. Most central office exchanges can handle up to 10,000 telephones. To connect more than 10,000 phones, or to connect phones in different cities, states or countries, a complex network of many telephone exchanges is used. It is called the Public Switched Telephone Network (PSTN). The PSTN operates under a hierarchy tree, which efficiently routes the calls. Telephone exchanges exist in the network hierarchy, in which the first four classes are usually for long distance switching, and the fifth class is for connection to the subscription telephones. The PSTN attempts to make connections at the lowest possible level, and therefore the shortest path. If the lines are busy, trunk groups at the next highest level are used.
Under the conventional telephony scheme, calling parties do not pay in advance or in real-time for the calls that originate from their telephone set. Rather, a telephone subscriber receives a bill, typically on a monthly basis, from the telephone company servicing that subscriber's calling area that lists the calls made during the prior billing period and the charges for each call. The subscriber is then required to provide the telephone company with the appropriate payment, typically by a check sent through the mail. A subscriber may also use a calling card, in which the subscriber is assigned a personal account number. The call is then billed to that account number. This enables a calling party to bypass the typical payment scheme for calls made at a remote location, such as a pay telephone. Calls made using a calling card are also accounted for in the subscriber's monthly bill from the telephone company.
Recently, there have been attempts to provide an alternative to conventional telephony means for initiating calls, routing and connecting calls, and payment. These attempts have been in the field of Internet telephony, which is the transmission of voice over the Internet. Voice includes voiceband-modulated data, facsimile signals and human speech. Internet telephony typically uses the Internet as an alternative to the PSTN to carry voice communications. This allows a conversation to occur from computer to computer, rather than from telephone to telephone. By exchanging voice packets in real-time, users may conduct inexpensive conversations over standard Internet connections. Presently available Internet telephony applications, however, are limited in that they provide services only to a small community of users and thus do not provide a viable alternative to the long-distance providers of the PSTN. For example, current systems require both the calling party and the receiving party to be equipped with multimedia personal computers (PCs) (i.e., PCs having a microphone, capable speakers, and a soundcard) and to be on-line at the same time so that the "connection" may be made through the server. Since calls can only be made from one computer to another, users must prearrange calls or they must always leave their Internet telephony application running on their PC. Existing systems fail to provide a mechanism for contacting a non-connected party, i.e., "ring" the non-connected party's telephone line. The community of available receiving parties is further limited by the fact that currently available software packages are generally incompatible. Existing systems also require the calling party to know the intermediary server's IP address in order to have a telephonic conversation over the Internet. Moreover, users are not provided with the opportunity to select among a plurality of servers that may be willing to handle the call.